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54
Using Tree Rings to Reconstruct Past Climates
Dendroclimatology is the study of the relationship between
tree growth and climate change. As a tree grows, it adds one
ring for every year of growth. The width of each growth ring
depends on a number of environmental factors, primarily
temperature and precipitation. Tree rings are a type of proxy
data: wide rings suggest wet years, while narrow rings imply
dry years.
The growth rings in a living tree represent a record of the recent
past. Since trees subject to similar environmental conditions
produce similar growth rings, comparison of growth rings
between trees of different ages, a process called cross-dating,
allows the data record to be extended into the distant past.
Scientists match a sequence of tree rings in one tree or log with
those in another tree or log to extend the record.
Douglas-fir tree rings from southwestern New Mexico.
1740
1770
1800
Year
1830
1860
Variance
1.5
Dendroclimatology has been used to reconstruct
El Niño variability over the past 700 years. El
Niño has a significant impact on precipitation in
Oregon. The red line reflects direct instrumental
measurement, while the blue line reflects precipitation estimates determined using tree ring data.
1.0
0.5
1300
1400
1500
1600
1700
Year
1800
1900
2000